It is known to provide a mounting structure for circuit elements in the form of a carrier of a flexible electrically insulating material formed on a surface with conductive strips effecting electrical connection between the circuit elements which are arranged on one side of the carrier. The carrier with the elements mounted thereon can be folded and/or rolled to minimize the volume occupied by the structure.
Such circuits can be provided in a variety of forms. For the purposes of the present invention, these circuits will be understood to be contactless (proximity) switches utilizing the principles set forth in U.S. Pat. Nos. 4,193,023 and 4,225,748, for example, so that the circuit elements can include externally affected oscillators or switching amplifiers, an oscillator or switching-amplifier controllable electronic switch, e.g. a transistor, a thyristor, a triac, etc., and a supply circuit for delivering the supply voltage for the oscillator and/or the switching amplifier.
Electronic proximity switching devices are required to deal with a number of electrical problems, e.g. the generation of the supply voltage, improvement of the oscillator or amplifier, switching pulse delay and short circuit resistance. They must also deal with a number of mechanical problems, an important one of which is the provision of the circuit elements in the smallest amount of space or, for a given space, the inclusion of the greatest number of circuit components.
In the circuit arrangement described in German patent document laid-open application DE-OS No. 19 40 373, these problems are partially solved by providing the electronic component carrier in a folded or rolled condition so that the components lie in a different planes within the housing. The space within the housing is optimally used and a high packing density is achieved with respect to the components.
A high packing density for electronic components can also be achieved with the arrangement described in German Pat. No. 31 23 372 (see U.S. Pat. No. 4,481,559) when the components on the thin carrier are applied on opposite sides of a flat auxiliary support. Here too a number of planes are provided for the arrays of the components and the housing space is better utilized.
In these systems, the conductive strips can be provided on the component side of the carrier, thereby affording the advantage that the carrier itself can form an insulating layer on the opposite side.
Electrical circuits of the type with which the present invention is concerned are extremely sensitive to external perturbation fields so that the need for shielding plays an important role in the design of such circuits. For this reason a metal housing or a housing with a high degree of shielding is generally provided. However, it has been found to be advisable to provide the circuitry with electronic shielding independently of the casing or housing.